1. Field of the Invention
This invention relates to a process for the continuous extrusion of electrically conductive granulated materials, preferably powder metallurgy materials, in which the material is introduced into a die and is compressed by the moving strokes of a punch in a die passage duct, against a frictional resistance which is built up by a section of the material strand already compressed therein, is advanced by the pressure of the compression stroke in the duct, is sintered on heating by electrical currents, and is extruded through a nozzle.
2. Description of the Prior Art
It is known (DE-AS No. 27 33 009) to continuously extrude powder metallurgy materials in a die and to heat the material by induction being provided within a certain zone in which the sintering of the compressed material takes place. The inductive eddy currents produced in these circumstances for heating the already compressed strand of material mainly result in heating of the metal dies used and are produced only to a minor degree on the surface of the conductive strand itself. The complete strand heating required for sintering thus takes place substantially solely by thermal conduction from the die or the outer surface of the strand to the interior thereof. Certain difficulties may occur in these circumstances so that the inner cross-sections of the strand are not always reliably reached or else relatively very different temperature zones occur, at least locally, within the strand of material. The effect of the induction heating is also restricted to the place where the electromagnetic field of the inductive heating installation acts on the strand. Furthermore, the relatively expensive induction heating system require a fairly large amount of space. In addition, inductive heating systems cannot be used for all electrically conductive materials, but only for those which are magnetizable.